3, Identification needed

Read more on the Acoustat 3 in our home audio section

Paul De Mink2004-02-23 22:21

Hi Andy, please excuse this long rambling post - feel free to edit for publication, should this be desired. However,I would have appreciated the details when struggling to identify the exact model, and am still not sure that my conclusions are accurate - hope you can help me some more. I have recently bought a tatty pair of what seem to be Acoustat electrostatic speakers. From some information contained elsewhere on this site, I believe they are the \'Model 3\', but some other info seems to contradict this. I will describe them in painful detail, hoping to you can ease my confusion and perhaps help some others. Each speaker consists of a large flat panel - from the top to almost the bottom is a cream-coloured fabric \'sock\', below this the panel is finished in a \'wood-print\' veneer. One of the speakers has, on this veneered footer, a badge which reads \'ACOUSTAT\'. Panel dimensions in millimetres / inches:

A problem here is that the pdf document \'9041CMACO-MAN-Model-1-3-1+1-2+2.pdf\' which seems to be an \'Owner\'s Manual and Assembly Instructions\' for Models \'1\', \'3\', \'1+1\' and \'2+2\', suggests that the Model 3 is 72 inches tall, which mine is not. Width and Depth seem to check out OK. Inside the panel, peering through the sock with a light behind it, there seem to be 3 distinct dark vertical shapes, which I imagine are the electrostatic panels proper. Behind the panel, firmly attached to the back of the veneered foot, is a black metal box which seems to function as an \'outrigger\' support, so the panel can stand almost upright. The back of this structure has many inscriptions, including:

There do not seem to be any support straps, as mentioned in one of the MK121 description documents, nor are there any \'medallion\' stickers. Black box dimensions in millimetres / inches(looking from the back of the panel):
This seems to match the very useful description and photo of the Model 3 posted by Bryan J. Minhinnett in March 2001.The ratio between height and width in his photo also matches mine (H/W = 2.08) Unfortunately, one of the panels (the one with the badge) plays MUCH softer than the other. I am afraid I will damage it, if I ignore this and simply adjust the balance control on my amplifier (South African-made Valve Audio Model 802 hybrid integrated 100W 6922 tube/MOSFET ), so I am trying to find someone with only 2 thumbs to investigate and hopefully fix it. But, what circuit diagram should I show them? The document \'Owner\'s Manual and Assembly Instructions\' for Models \'1\', \'3\', \'1+1\' and \'2+2\' has a pic labeled \'MK 121\' while the document \'The MK-121-2(A) Medallion (C) Mod\' has a pic labelled \'MK-121C\' I suspect mine is somewhere between the two - is this so? Which can I say is closer? Please accept my thanks for all the time and trouble you\'ve obviously put into this site already, even if you can\'t help me specifically. Similarly, I\'d like to thank the other posters who have shared their experiences, knowledge and enthusiasm. Regards, Paul de Mink, Cape Town, South Africa


Andy Szabo2004-02-23 22:21

One of my pet peeves about pre-Spectra Acoustat is that the speakers were never labeled with the model number. The only identification was the interface style, which, of course, could be used with several different models. This problem is most severe with three-panel speakers, since this configuration was used throughout Acoustat\'s history, appearing in several different forms. Under ”Pictures” you can see at least two of the variations that were all called ”Model 3”. You have an early Model 3 with the full-range MK-121-2A interface and the wood-grained section at the bottom of the panel. Later Model 3\'s had the grille cloth all the way to the bottom. Since your speaker lacks any Medallion labels, you can probably assume that the interfaces were never modified with the new transformers. (Note: look at the two audio transformers. If they have black paper wrappers, then they are Medallion. If they have brown paper wrappers, then they are the originals.)

The electrical schematic shown in the owner\'s manual ”Model 1, 1+1, 2+2 and 3” should be very similar, if not identical, to what you have. The schematic shown is pre-Medallion ”C”. If you have determined that you do have Medallion transformers, then use the schematic shown in ”MK-121-2A Medallion ”C” Modification”.

I would be cautious in using your speakers if one is significantly lower volume than the other. There is obviously something wrong. If the attenuation seems even across the audio range, I would suspect a problem with the bias power supply. If only the lows are attenuated, look at the low-frequency transformer and associated components. If only the highs are rolled off, then look at the high-frequency transformer and associated circuitry.

Also check for corrosion on the high-frequency balance control. This part is notorious for corrosion, often covered with either a green or white ”fuzz”. This can be cleaned with fine emery cloth. The Monster Cable is also known to oxidize, turning green inside its plastic jacket. This is largely a cosmetic problem, although if the oxidation is great enough, the soldered connections may be compromised. You\'ll probably want to eventually replace the Monster Cable, but I doubt it is the cause of your immediate problem.

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